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\section{Introduction}  There is abundant evidence that pore fluids and fracture processes in the upper crust are physically and chemically coupled (\citep{Hubbert:1959ea, Frank:1965wi, Nur:1973ju, Sibson_1981}. (\citep{Hubbert:1959ea,Frank:1965wi,Nur:1973ju,Sibson_1981}.  Increases in pore fluid pressure, for example due to fluid injection, can lead to rupture and an increase in seismic activity. This is readily explained by the Navier-Coulomb criteria for brittle failure and the decrease in effective stress as a result of the elevated pore fluid pressure \citep{Price:1966uh, Sibson_1981}. \citep{Price:1966uh,Sibson_1981}.  Conversely, the changes in groundwater levels and the surface effusions of warm water that sometimes occur along fault traces following earthquakes show that failure can also have a profound effect on fluid flow, heat and mass transport \citep{Nur:1974ht, Sibson:1975cn, Sibson_1981}. \citep{Nur:1974ht,Sibson:1975cn,Sibson_1981}.  The flow is interpreted to result from either seismic pumping as a result of dilatancy diffusion type processes or a seismic valve mechanism in which fault rupture leads to leakage of an overpressured aquifer or reservoir of fluid \citep{Nur_1972, Sibson_1981}. \citep{Nur_1972,Sibson_1981}.  In the geological record direct evidence for episodic and rapid flow of fluids associated with fracture and faulting is more equivocal. The presence of banded hydrothermal mineralisation of varying degrees of complexity in exhumed fault systems is often taken as evidence of pulsed fluid flow driven by seismic activity. Failure often results in brecciation of earlier generations of veins and the opening of large dilation voids that are then cemented by mineral precipitation from upwelling hydrothermal fluids \citep{Wright:2009ej}. The extent, however, to which mineral precipitation in the veins is contemporaneous with, and directly coupled to failure is open to question. Observations of epithermal mineralisation associated with dilation jogs between en-echelon fault segments suggests that in this structural setting fluid flow is rapid, being accompanied by rapid pressure fluctuations which triggers high level boiling, or effervesence of hydrothermal fluids. This results in precipitation of common gangue quartz and calcite as well as economic metalliferous deposits \citep{Sibson:1975cn, Sibson:1987dq, Henley:2000wn}. \citep{Sibson:1975cn,Sibson:1987dq,Henley:2000wn}.  A characteristic feature of systems with episodic pulsing of warm to hot fluid is the development of a thermal anomaly along the high permeability paths in which flow is focused. An example is the perturbation of the temperature field observed in Mississippi Valley Type (MVT) districts that lie around the upper Mississippi Valley and other major Palaeozoic sediment basins in the continental USA \citep{Sangster:1994ub}. Similar temperature anomalies have been reported for other sedimentary basins, for example to the south east of the Massif Central in France \citep{Charef:1988vt}. The anomaly is seen as a difference between the temperature of precipitation of hydrothermal minerals and that of the of the host rock at the depth of burial and time that the mineralization took place. Using simple thermal modelling Cathles and co-workers show that that the temperature difference is due to heat advection associated with episodic, rapid release of hot fluids from deeper regions of the basins \cite{Cathles:1983tj, CathlesIII:2005uo}. \cite{Cathles:1983tj,CathlesIII:2005uo}.  In these example the fluids are thought to originate from overpressured brines in compacting sedimentary basins. Importantly, the fluid velocities required to produce the thermal anomaly are more than 1000 times greater than could be produced by the steady subsidence, compaction, and dewatering of the basins \citep{Cathles:1983t}. This suggests to us that the pulses result from a coupling between the pore fluid pressure and rock failure. We envisage that when pore fluid pressures approach lithostatic either mode I hydraulic fracturing or shear failure and development of dilation jogs along fault surfaces allows rapid dewatering of the sediment pile with channel flow of fluids into, and along thin aquifers. To help us understand these processes we have used clumped isotope thermometry to determine the temperature at which hydrothermal vein calcite precipitated in dilation voids of a Variscan strike-slip fault in the southern Pennines of the United Kingdom. The veins are associated with Pb-Zn and fluorite mineralisation and the fault was extensively worked as an economic deposit. Located at the margin of a lower Carboniferous platform on which shelf carbonates were deposited, the fault separates the platform from a deep water basin infilled with deep water facies limestones and shales of lower to upper Carboniferous age.